The present invention relates to servo information for magnetic storage devices and, more particularly, to writing servo information to disks during the manufacturing process.
Magnetic heads are used to read data from and write data onto certain data regions of magnetic disks. To accurately perform these operations, it is important that the heads be properly positioned over the data regions. Servo-systems are conventionally used in an attempt to ensure the proper positioning of the heads relative to the data regions. Servo-systems sense the position of the heads and generate position error (xe2x80x9cPESxe2x80x9d) signals to adjust the position of the heads to their respective proper locations over the magnetic disks. The PES signal is generated from a predefined servo pattern which is located at certain points on the disk surface, and will be discussed in more detail below.
A standard disk drive, generally designated 10, is illustrated in FIG. 1. The disk drive comprises a disk 12 that is rotated by a spin motor 14. The spin motor 14 is mounted to a base plate 16. An actuator arm assembly 18 is also mounted to the base plate 16. The actuator arm assembly 18 includes a head 20 mounted to a flexure arm 22, which is attached to an actuator arm 24 that can rotate about a bearing assembly 26. The disk drive 10 also includes a voice coil motor 28 which moves the head 20 relative to the disk 12. The spin motor 14, voice coil motor 28 and head 20 are coupled to a number of electronic circuits 30 mounted to a printed circuit board 32. The electronic circuits 30 typically include a read channel chip, a microprocessor-based controller and a random access memory (RAM) device.
The disk drive 10 typically includes a plurality of disks 12 and, therefore, a plurality of corresponding actuator arm assemblies 18. However, it is also possible for the disk drive 10 to include a single disk 12 as shown in FIG. 1.
Referring now to FIG. 2, data is stored on the disk 12 within a number of concentric radial tracks 40 (or cylinders). Some tracks 40 may solely contain servo information, while other tracks may contain both servo information and data. Typically, however, tracks 40 contain both servo information and data. Each track 40 is divided into a plurality of sectors 42. In tracks 40 which contain both servo information and data, each sector 42 is further divided into a servo region 44 and a data region 46.
The servo regions 44 of the disk 12 are used to, among other things, accurately position head 20 (the head 20 is shown in FIG. 1) so that data can be properly written onto and read from the disk 12. The data regions 46 are where non-servo related data (i.e., user data) is stored and retrieved. Such data, upon proper conditions, may be overwritten.
Each track 40 has a centerline 48. To accurately write and read data from the data region 46 of the disk 12, it is desirable to maintain the head 20 in a relatively fixed position with respect to a given track""s centerline 48 during each of the writing and reading procedures. For simplicity and for purposes of demonstrating the invention, it will be assumed that the head 20 should be positioned on, or substantially on, a given track""s centerline 48 to accurately read data from and write data to the data region 46 of that track 40. It should be noted, however, that the invention described herein is equally applicable to those systems which incorporate a read or write offset from the track centerline, as will be understood by those skilled in the art.
To assist in controlling the position of the head 20 relative to the track centerline 48, the servo region 44 contains, among other things, servo information in the form of servo patterns 50 comprised of groups of servo bursts A, B, C, D as shown in FIG. 3. The servo bursts A, B, C, D are accurately positioned relative to the centerline 48 of each track 40, are typically written on the disk 12 during the manufacturing process using a servo track writer (xe2x80x9cSTWxe2x80x9d) and, unlike information in the data region 46, may not be over-written or erased during normal operation of the disk drive 10.
As shown in FIG. 3, the A and B burst pairs define what are conventionally known as the Norms. The difference in amplitude between the A and B bursts at a particular head position is defined as the Norms signal (in units of volts) and is represented by N=Axe2x88x92B. A Norms curve can be developed to represent Norms signals for head positions across an entire track. Likewise, the C and D burst pairs define what are conventionally known as the Quads. The difference in amplitude between the C and D bursts at a particular head position is defined as the Quads signal (in units of volts) and is represented by Q=Cxe2x88x92D. A Quads curve can be developed to represent Quads signals for head positions across an entire track.
Traditionally, during the manufacturing process of the disk drive 10, a servo-track writer (not shown) is used to write servo information, including servo bursts A, B, C, D onto each of the servo regions 44 of the disk 12. The servo track writer includes its own write heads which are used to write the servo information to the disks prior to the disks being sealed within the disk drive. The servo track writer is a highly specialized, and high-priced piece of equipment which writes the servo bursts at precise locations on the disk surfaces. It would therefore be advantageous to use as few servo track writers in a manufacturing production line as possible in order to reduce capital costs of additional servo track writers.
As will be understood by those of skill in the art, disk drives are generally manufactured in clean rooms, which provide a manufacturing environment that is largely free of external contamination. Because disks may be exposed during the manufacturing process, it is important to reduce external contamination. External contamination on a disk surface can, in certain situations, damage or degrade the performance of a disk drive. As part of the manufacturing process, the servo-track writer is located in the clean room with the other manufacturing tools which require a clean room environment.
Clean rooms are generally very expensive to construct and operate. Constructing a clean room requires sophisticated manufacturing techniques which are more expensive than construction techniques used for standard, non-clean room construction. Additionally, clean rooms require sophisticated air handling and filtration hardware, which adds to the cost of construction as well as operating costs. Accordingly, it would be advantageous to minimize the size of a clean room, and thus reduce the capital costs of construction and operating costs.
As disk drive technology progresses, more and more information is able to be stored onto a single disk. Accordingly, the number of tracks per inch on a disk is continually increasing. As discussed above, tracks have associated servo information. Therefore, when additional tracks are included on a disk, additional servo information must be written to each disk. This requires additional time for each disk to be in the servo track writer. As a result, additional servo track writers are needed to support the same build rate of drives on a production line as track density increases. Additional servo track writers result in additional capital costs for both the additional equipment, and the additional clean room space required to house the additional equipment. Furthermore, the additional servo track writers may be difficult to fit into an existing facility, possibly resulting in a reduced output capacity for a facility as track density increases.
Some existing solutions to the problem of trying to reduce the number of servo track writers located in a production line are to pre-write disks prior to the manufacturing process which incorporates the disks into disk drives. Such pre-writing may be bulk writing of media to record the servo information, or printing the media using a magnetic printing process to record the servo information on the disks. In both of these solutions, additional equipment is required to write the servo information to the disks. Pre-writing disks requires equipment to write the information on the disks prior to the disk drive manufacturing process. While this is an available alternative, which may save space in a factory, it still requires the capital expense of the writing equipment. Additionally, many manufacturers have an existing investment in servo track writers which are located in factories. Thus, converting to a different type of machine to write servo information would result in a loss of value for the existing installed base of servo track writers. As described above, servo track writers are highly specialized pieces of equipment which have a significant cost. Thus, it would be beneficial for many manufacturers to continue to use their installed base of servo track writers, while increasing the production capacity of such installed base.
Accordingly, there is a need to develop a method for writing servo information to a disk which (1) reduces servo track writer time relative to conventional servo track writing procedures, (2) accurately and reliably writes the servo information to the disk, and (3) requires little or no additional clean room space to accomplish. The present invention, among other things, is designed to meet the aforementioned needs and to overcome the aforementioned problems.
The present invention relates to a method for encoding servo information onto a hard disk of a hard disk drive. The method requires only a portion of the servo information to be written during the clean room manufacturing process, with the remaining servo information written by the disk drive after assembly. By writing a portion of the servo information during the clean room manufacturing process, fewer servo track writers are required for a given build rate than would be required if all servo information were written during the clean room manufacturing process. This results in a requirement of fewer servo track writers for a given capacity of the manufacturing line, resulting in reduced capital costs for both equipment and clean room space. In addition, the servo track writers occupy less area within the clean room, thus allowing for additional production capacity for a given clean room area.
To achieve the above benefits, the servo track writer writes the gray code, and A, B, C, and D servo bursts for a first number of tracks, and the servo track writer writes the gray code, A and B servo bursts for the remaining tracks. The disk drive is then sealed, and the remaining C and D servo bursts are written to the disk using the read and write heads of the disk drive. Within the disk drive, the read and write heads are situated such that the path of the write head will not overlap the path of the read head for any data track on the disk surface.
When writing the remaining C and D servo bursts, the read head is located in a position ahead of the write head. The read head reads the servo information for a first track, and the position of the actuator arm is adjusted based on the read servo information. The write head is then used to write the C and D servo bursts to a second track. In one embodiment, the read head reads a first servo sector on a first track, the position of the actuator arm is adjusted, and the write head is writes the C and D servo bursts for a second servo sector on a second track. This pattern is continued until all of the servo sectors have been written.
When adjusting the position of the actuator arm, the control electronics within the disk drive move the actuator arm such that the read head is in a default position with respect to the first track by using a default reader-writer offset value. The A, B, C, and D servo bursts from the first track are read by the read head. Track spacing error is calculated based on the magnitude of the signal of the A, B, C, and D servo bursts. A compensation value is calculated based on the spacing error, which is then added to the reader-writer offset value. The position of the actuator arm is then adjusted based on the new offset value. The C and D servo bursts for the second servo sector on the second track are then written.